Electric amplifier circuits



March 17, 1942. F, sAq-q AL 2,276,417

V V ELECTRIC AMPL FIER CIRCUIT I Filed Sept. 30, 1938 3 Sheets-Sheet 1we): in ma I Jlttmmys 3 Sheets-Sheet F. PREISACH ETAL ELECTRIC AMPLIFIERCIRCUIT Filed Sept 30,- 1938 March 17, 1942.

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Mafch 17, 1942.

F. PREISACH ET'AL ELECTRIC AMPLIFIER CIRCUIT 3 Sheets-Sheet 3 FiledSept. 30, 1938 flitarnays F atenteoi tiller. 3?, 3. 32

I 2,276,417 v amcrnrc AMPLHHER CllRCill'iS Fcrenc lreisacli and HmreZakarias, Budapest,

Hungary, assignors to Vereinigte Gliihlampen. und Elelxtrizlt'atsAiktiengescllschaft of Uihest;

near Budapest, Hungary Application September '30, 1938, Serial No.232,676

err

attest? tea in Germany September 30, 1932 12 Claims.

Amplifier tubes having an electron multiplying action are known aselectron multiplier tubes. In these tubes the primary electrons emittedby a cathode are controlled by a control. grid and accelerated by ascreen grid, whereupon they impinge on a multiplying electrode and theregive rise to a secondary emission, the relatively large number ofsecondary electrons thus released passing to the working anode.

The present invention relates to the use of tubes of this kind inamplifier circuits, but it is not concerned with the construction of thetubes themselves or of the multiplying electrodes which they contain.Thus the tubes hereinafter re-.

ferred to have only one multiplying electrode but it will be obviousthatthe invention can equally well be applied in the case of tubes with aplurality of such electrodes.

It is characteristic of the working of thesetubes that their anodecurrent is derived from two sources; (1) from the primary thermalemission of the incandescent cathode and (2) from the secondary emissionof the multiplying electrode.

If we d'efine as positive current the direction of the anode current ofan ordinary electron tube (that is to say, the direction opposite, tothat in which the electrons travel) weshall have, in a multiplier tube,two electrodes with a neganished by the voltage source coincides inpractice with the voltage OF at which the sign of the multiplyingelectrode current reverses. However the magnitude of this voltage OF isindica tive of the secondary emission'properties of the multiplyingelectrode, as it indicates at what velocity of the electrons the numberof the secondary electrons will be equal to the number of the primaryelectrons. When supplying the multiplying electrode from a source ofvoltage through a series resistance, care must be taken that the minimumno-load voltage exceeds the valueOF. On the other hand the no-loadvoltage of the source must not, exceed the working voltage 0A. As the.working voltage of the multiplying electrode must be less than the anodevoltage, it is an obvious expedient to obtain the voltage of themultiplying electrode from the higher anode voltage by means of avoltage ditive current, i. e. the incandescent cathode and thepositively charged multiplying electrode.

It is the object of the present invention to provide circuit conditionswhich make allowance for the aforementioned unusual conditions underwhich the anode current is derived-and to enable stable and efilcientworking to be obtained. The

voltage current characteristic of a multiplying electrode is the wellknown dynatron characteristic-shown in Fig. 1 of the attached drawings.

To ensure a stable working point, it is necessary to derive the terminalvoltage of the multiplying ele'ctrodefroma source having an internalresistance which is less than a critical maximum value.

This value can be read off in said vider circuit. The dimensioning ofthe voltage divider is determined in accordance with the forc goingconsiderations, by the fact that under no load (when the electrode iscarrying no current) the voltage of the multiplying electrode exceedsinput circuit, 9 is the cathode resistance, it and I 3 are decouplingcondensers, and ii and 82 are resistances which constitute the voltagedivider Fig. 1, in the usual way, from the reciprocal value of the slopeof the straight line CDE, indicating the critical resistance. Theworking point C can be adjusted either by using a source .of voltage 0A,the internal resistance of which is practicallyzero. or else by using asmaller voltage OB and a series resistance, the value of whichis'indicated by the straight line BC. 'The limit for stable working isthe use of a source of voltage OD in conjunction with a resistancegraphically depicted by the straight line CDE.

for the screen grid voltage. Further, it is the anode resistance and I 5is the coupling condenser in the output circuit. The voltage divider forfeeding the multiplying electrode is constituted by. the resistances E7and it, the resistance it being provided with an alternating currentshunt.

through, the condenser is. The input is denoted byI, I and the outputjoy 0. 0'. of the incandescent cathode need not be described but anindirectly heated cathode is shown. The source of voltage is connectedto the terminals -V,, V.

'A suitable dimensioning of. the voltage divider in accordance with thisinvention will now be described. If, for example; the voltage of thesource The minimum no-load voltage OD tobe' furof of energy amounts to400 volts, the voltage on the Also, I is the grid leak resistance, 8 isthe coupling condenser in the The heating eter or voltage divider mustbe 177,000 ohms, the

component resistances l1 and I6 having the values 35,400 ohms and141,600 ohms, respectively and the consumption will be 0.4 watt. It theworking of the tube is to be made less dependentupon the current, takenby the multiplying electrode, the resistances must be smaller and theno-loadvoltage higher, in which case the consumption of energy will begreater. As a second used to supply anode direct current for other(ordinary) electron tubes having a working anode voltage which coincidesvery nearly with the working voltage on the said multiplying electrodeor electrodes. The multiplying electrodes may work in parallel with avoltage source'such' as a mains rectifier to supply direct currentenergy for the same consumers;

. Fig. 3 shows an example of a circuit comprisingthree electronmultiplier tubes I, I, I" andan multiplying electrode 250 volts and thecurrent dividers are used, it is necessary to add on to the voltagedivider consumption of 1.2 watts the consumption due to the anodecurrent of the output tube, which amounts to 400'voltsX40 mA.=16 watts.The increase is nearly 50%. In addition'to the saving in current,however, the circuit shown in Fig. 3 ensures greater stability because,owing to the low voltage divider resistances, the working currents areless dependent on the characteristics of the tube.

In th circuit arrangement shown in Fig. 4,

a separate source or voltage V +V' is provided for the supply to theanodes of the multiexample, assuming that'the operating voltages pliertubes, so that a series resistance becomes superfluous. If the currentconsumption of the ordinary electron tube or tubes is too mjaall, it

may happen that the'demand for an adequately high no-load. voltage whenthe multipliers are example shown in Fig. 3 and the loadingresistordinary amplifying tube 20, employed as an output tube. Inaddition to the circuit elements, which are shown with th same.reference symbols as in Fig. 2, condensers l8, l8 and i8" play the samerole as IS in Fig. 2, while l0, l0 and I9" severally denote chokes fordecoupling the multiplying electrodes. In this figure, additionally, 2|denotes the incandescent cathode, 22 the control grid, 23 the screengrid, 24 thesuppressor grid and 25 the anode of the output tube 20, forwhich 20 is the grid leak resistance. Further,

. 2'! is the cathode resistance, 28 and 30 decoupling condensers and 3 Iis the anode resistance. The multiplying electrodes of the electronmultiplier tubes are connected to the point or supply Sp for the anodeof the ordinary electron tube. This point of supply Sp is connectedthrough the resistance 28 to the pole oi the source of voltage. It theoperating data for the multiplier tubes is assumed to be the same as inthe fore-- going example (multiplying electrode voltage.250 volts, anodevoltage 400 volts, multiplying 'electrod current 6 mA.) we get back fromthe three tubes 3x6=18 mA., which, for a voltage of 250, means aneconomy of 4.5 watts in power consumption. The additional consumption inthe resistance 29, "which constitutes the second part of the voltagedivider, amounts to 150 volts 22 mA.=3.3 watts i1 40 mA. anode currentis assumed for the output tube. In the alternative arrangement in whichthe multiplying electrodes are supplied by separate voltage dividers,there must be added to the calculated potentiometer consumption of the'first example (3X0.4=1.2

watts. On the other hand, when separatevoltage ance 32 in the exampleshown in Fig. 4 can be replaced by the field coil or a loud speaker. Itis also possible to utilise the consumer resistance in connection with32 of Fig. 4 as a voltage dividerior supplying any electrodes of thetubesof the amplifying circuit which require a lower supply voltage. I

The circuit conditions thus far describedserve to economise in thecurrent consumption of multiplier tubes'while ensuring their stableworking able variations in the characteristic curves of the tubes duringworking or due to diflerences in individual tubes is adequatelycompensated,

so that such defects are minimised as far as possible.

As is well known, the ordinary commercial amplifier tubes show deviationin the sense that the anode-current grid-voltage curves tend to paralleldisplacement around a certain grid voltage value. In the usual circuits,the shifting or displacement of the working point caused in this way ispartially compensated by not using a fixed grid bias but making the gridbiasing voltage proportional to the cathode current. This condition iseasily attained by using a cathode resistance, the voltage drop in whichprovides the grid bias. Inmultiplier tubes however, the anode current isderived only in part from the primary cathode current and is due mainlyto the current of the multiplying electrode. Thus, ii only the ordinarycathode resistance were used, fluctuations of the primary current wouldbe compensated, but not those of the secondary current. It would,however, be desirable, when the multiplying electrode current decreases(owing, for instance to a reduction in the secondary emission) for theanode current to be increasedautomatically, as, for example, by areduction of the bias on the control grid.- These conditions can beobtained, according to the 1 output anodes amountsto 40 0 volts 22mA.=8.8

.. present invention, by a circuit arrangement such as that which isshown diagrammatically in Fig. 5.

' The characteristic feature of thecircuit shown in said Fig. 5 is thatthe multiplying electrode is connected not only to a -positive feedpoint,

through resistance l6, but also to the cathode, through a resistance 33.The cathode resistance 9 is traversed, both by the cathode current andby that part of the current of the multiplying electrode which flowsthrough the resistance 33. If then the multiplying electrode currentdiminishes while the tube is in use, the voltage on this electrode and,therefore, the current passing through the resistance 33, will be lessand so also will be the current passing through current and the anodecurrent of the tube are increased. I

It is possible to render such a compensation for avoiding unwantedvariations of direct current still more efiicient by making the cathoderesistance as large as possible compared with the reciprocal value ofthe slope of the multiplier tube. In order to adjust the grid biascorrectly when the value of the cathode resistance is high, it isnecessary for the direct current grid connection to be taken to a pointthe potential of which is positive in relation to the negative terminalof the source of voltage. In the example shown in Fig. 5 this is done bycon-. necting the grid not only (as usual) through a resistance 1 to thenegative terminal V of the source of voltage, but also through a higherresistance 34 to the'positive terminal +V of the same source V +V. Thevoltage divider formed by the resistances I and 34 determines thevoltage of the control grid in relation to the negative terminal V ofthe source of voltage. Amplifier circuits according to this inventioncan with advantage be incorporated in television receiving apparatus andin such cases the source of voltage for the anodes of the electronmultipliers can be used simultaneously for supplying the defiectors orsweep voltage devices for line and frame scanning in the picture tube.

What we claim is:

1. An amplifier circuit including at least one.

electron multiplier tube therein having an emissive source of primaryelectrons, a control grid,

a screen grid, a multiplying electrode, and an 3 output anode, togetherwith means for heating said emissive source, said amplifier circuitfurther including one or more amplifier tubes following said multipliertube, characterized by the fact that said circuit is provided with meansconstituting a voltage divider for the D. C. current feed to themultiplying electrode of said tube and with means constituting a voltagedivider for the screen'grid voltage thereof, the first-named dividerbeing so proportioned or dimensioned and operable that for zero currentin said multiplying electrode the accelerating voltage on the same has avalue which exceeds fifty volts with reference to the emissivesource,but is less than the working voltage 'for said multiplying electrode,said multiplying electrode being connected with the anodes, of saidamplifier tubes in such a way that the current yielded by themultiplying electrode is used in part or wholly for the supply of anodedirect current to other amplifier tubes placed in the circuit.

2. An amplifier circuit according to claim 1, including also a source ofdirect current connected in parallel with a multiplying electrode of amultiplier tube so that the multiplying electrode and the source ofdirect current act as parallel sources of energy for at least oneconventional amplifier tube in the amplifier circuit. 3. An amplifiercircuit including at least one electron multiplier tube therein havingan .emissive source of primary electrons, a control grid, a screen grid,a multiplying electrode, and an output anode, together with means forheating said-emissive source, characterized by the fact that saidcircuit is provided with means constituting 'a voltage divider for thefeed to the multiplying electrode of said tube and with meansconstituting a voltage divider for the screen grid voltage thereof, thefirst-named. divider being so proportioned or dimensioned and operablethat for zero current in said multiply- .ing electrode the acceleratingvoltage on the same has a value which exceeds fifty volts with referenceto the emissive source, but is less than the working voltage for saidmultiplying electrode, said circuit including also at least one otheramplifying tube connected with said multiplier-tube, saidother'amplifying tube having.

a separate voltage source for its anode and said multiplying electrodebeing connected with the anode of said amplifier tube in such a way thatthe current yielded by the multiplying electrode is used in part orwholly for the supply of anode direct current to same.-

4. An amplifier circuit including therein at least one electronmultiplier tube having each atleast one multiplying electrode, anemissive source of primary electrons together with means for heatingsaid source, a control grid, an accelerating grid and an output anode,said amplifier circuit further including at least one conventionalamplifier, and said multiplying 'electrode being connected with theanode of said conventional amplifier, further characterized by the factthat said circuit is provided with means constituting a voltage dividerfor the feed of potential to said multiplying electrode of the v saidtube, the said voltage divider being so proportioned or dimensioned andarranged that for zero current in said multiplying electrodeof said tubethe accelerating voltage on the same has a value which exceeds fiftyvolts with reference to the emissive source, but is less than theworking voltage for said multiplying electrode, the current yielded bysaid multiplying electrode being used in part or 'wholly for the supplyof anode direct current to said connected amplifier.

5. An amplifier circuit including therein at least one electronmultiplier tube having at least one multiplying electrode connected withthe anode of at least one conventional amplifier included also therein,a common sourceof anode direct current for said multiplier tube and saidamplifier, said circuit being characterized by the fact that it isprovided with means constituting a voltage divider for the feed ofpotential to sai'djmultiplying electrodeof the said multiplier tube andwith means constituting :1. voltage divider also for the screen gridvoltage of said tube, the first-named voltage divider being soproportioned or dimensioned and operably arranged that for zero currentin said multiplying electrode of said tube the accelerating voltage onthe same has a value which exceeds fifty volts with reference to theemissive source, but

- is less than the working voltage for said multiplying electrode, saidmultiplying electrode being connected with the anode of said amplifiertube in such a way that the current yielded by said multiplyingelectrode is used in part or wholly for the supply of anode directcurrent to said connected amplifier.

6. An amplifier circuit including therein at least one electronmultiplier tube having at least one multiplying electrode connected withthe anode of at least one conventional amplifier included also therein,a separate source of anode direct current for said amplifier, saidcircuit being characterized by the fact that it is provided with meansconstituting a voltage divider for the feed of potential to saidmultiplying electrode of the said multiplier tube and with meansconstituting a voltage divider also for the screen grid voltage of saidtube, the first-named voltage divider being so proportioned ordimensioned and operably arranged that for zero current in saidmultiplying electrode of said tube the accelerating voltage on the samehas a value which exceeds fifty volts with reference to the emissivesource, but is less than the working voltage for said multiplyingelectrode, said multiplying electrode being connected with the anode ofsaid amplifier tube in such a way that the current yielded by themultiplying electrode is used in part or wholly for the supply of anodedirect current to said connected amplifier.

'I. An amplifier circuit having therein at least one electron multipliertube and at least one other amplifier tube, characterized by a provisionof means in said circuit for effecting the feed to the multiplyingelectrodes of said tube in such a way that for zero current in the saidmultiplying electrodes the accelerating voltage on the latter has avalue which exceeds fifty volts with reference to the primary cathode inthe case of a single or the first multiplying electrode and withreference to the preceding multiplying electrode in the case ofsuccessive multiplying electrodes, but is less than the working voltagefor said multiplying electrodes, said multiplying electrodes beingconnected to the anode of said amplifier tube in such a way that thedirect current yielded by the multiplying electrodes is used wholly orin part for the supply of anode direct current to other said amplifyingtube.

8. An amplifier circuit according to claim 1, including also anauxiliary resistance connected in parallel with the anode circuit of aconventional amplifier tube receiving anode direct current from amultiplying electrode of a multiplier tube, whereby to ensure stableoperating conditions in which the total current consumption in alloperating circumstances adequately exceeds the current delivered by themultiplying electrode.

- 9. An amplifier circuit including a'plurality oi electron multipliertubes each having an emis sive source of primary electrons, a controlgrid, an accelerating grid, a multiplying electrode. and an outputanode, together with means for heating said emissive source, saidamplifier circuit further including an ordinary amplifier tube employedas an output tube, the energy supplying circuits of said multipliertubes being connected in parallel with the anode feed circuit of trodes,the parallel connection of the energy supplying circuits of saidmultiplier tubes with the anode feed circuit of said ordinary amplifyingtube constituting one part of said voltage divider and the other partthereof being constituted by an ohmic resistance such for example as thefield coil of a loud speaker, the positive terminal of the D. C, supplybeing connected through the ohmic resistance to the common supply pointof the tubes.

10. An amplifier circuit wherein an additional source of voltage isprovided for th anodes of the multiplier tubes.

11. An amplifier circuit according to claim 1,- further characterized bya resistance between the, multiplying electrode and the cathode of thesame multiplier tube, said resistance being proportioned or dimensionedso that a portion of the current supplied by said multiplying electrodeis passed through the cathode resistance of said tube.

12. An amplifier circuit according to claim 1, wherein a grid biasingresistance is included in the anode circuit of the multiplier tubeand-the multiplying electrode is connected to the emissive source ofprimary electrons through said resistance of such a size that the valuesof the grid bias to the variations of the multiplying electrode currentso as to attain stable conditions.

FERENC PREISACH.

IMRE ZAKARIAS..

according to claim -9.-

are automatically regulated according

